本文转载www.helloweba.com 谢谢写这个代码的人
实现刮奖效果 使用 html5
实现效果：
代码如下：
<!DOCTYPE> <html> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width;initial-scale=1.0"> <title></title> <style type="text/css"> .demo{ width: 320px;margin: 10px auto 20px; min-height: 300px; } </style> </head> <body> <div class="demo"> <canvas></canvas> </div> <script type="text/javascript"> var bodyStyle = document.body.style; bodyStyle.mozUserSelect = "none"; bodyStyle.webkitUserSelect = "none"; var img = new Image(); var canvas = document.querySelector("canvas"); canvas.style.backgroundColor = "transparent"; canvas.style.position = "absolute"; var imgs = ['p_0.jpg',"p_1.jpg"]; var num = Math.floor(Math.random()*2); img.src = imgs[num]; img.addEventListener("load", function(){ var ctx; var w = img.width, h = img.height; var offsetX = canvas.offsetLeft, offsetY = canvas.offsetTop; var mousedown = false; function layer(ctx){ ctx.fillStyle = "gray"; ctx.fillRect(0,0,w,h); } function eventDown(e){ e.preventDefault(); mousedown = true; } function eventUp(e){ e.preventDefault(); mousedown = false; } function eventMove(e){ e.preventDefault(); if(mousedown){ if(e.changedTouches){ e = e.changedTouches[e.changedTouches.length -1]; } var x = (e.clientX + document.body.scrollLeft || e.pageX) - offsetX || 0, y = (e.clientY + document.body.scrollTop || e.pageY) - offsetY || 0; with(ctx){ beginPath() arc(x,y,10,0,Math.PI * 2); fill(); } } } canvas.width = w; canvas.height = h; canvas.style.backgroundImage = 'url('+img.src+')'; ctx = canvas.getContext("2d"); ctx .fillStyle = "transparent"; ctx.fillRect(0, 0, w, h); layer(ctx); ctx.globalCompositeOperation = "destination-out";//在源图像外显示目标图像。只有源图像外的目标图像部分会被显示，源图像是透明的。 canvas.addEventListener("touchstart", eventDown); canvas.addEventListener("touchend",eventUp); canvas.addEventListener('touchmove', eventMove); canvas.addEventListener("mousedown", eventDown); canvas.addEventListener("mouseup", eventUp); canvas.addEventListener("mousemove", eventMove) }) </script> </body> </html>